Measuring and Modeling Regional Sediment and Nutrient Fluxes of Floodplains and Streambanks, from Mountains to the Sea
Abstract
Floodplains and streambanks play a key role in watershed nutrient and sediment transport and stream water quality; however, current understanding and tools are insufficient to make spatially-explicit predictions of their fluxes of sediment and nutrients. We implemented the USGS Chesapeake and Delaware Floodplain Network to measure the deposition and erosion of sediment and associated nutrients for streams and rivers throughout the US mid-Atlantic, with the goal of identifying predictors of reach-scale material fluxes. We measured bank erosion and floodplain deposition over long time scales using dendrogeomorphology, sediment characteristics, and reach geomorphology along 68 stream reaches across the diversity of geology and land-use in the region. The magnitude of measured fluxes of sediment and associated N, P, and C of floodplains or streambanks did not differ across Valley and Ridge, Piedmont, and Coastal Plain physiographic provinces, but very small fluxes were measured in the mountainous Appalachian Plateau. The median sediment flux of floodplain deposition exceeded streambank erosion, with 34 of 58 completed sites being net depositional, and a few sites had substantial floodplain deposition. We are developing regression models that use upstream watershed attributes and reach-scale geomorphometry to scale measured fluxes to the larger regional network of reaches. Preliminary models for the Chesapeake show very high predictability of fluxes (>90% of spatial variance explained) that enable predictions of floodplain and streambank fluxes for each of its 81,069 NHDPlus stream reaches. Summing these predicted fluvial fluxes, along with predictions of upland erosion and measured river loads, generates high-resolution sediment and associated N and P budgets for the region's watersheds. The sediment budget demonstrates that streambank erosion and floodplain deposition loading exceeds measured river loads by a factor of two. In conclusion, the fluvial exchange of sediment between streams and floodplains is critically important for understanding watershed sources, sinks, and transport of sediment and nutrients. Our approach for measuring and modeling floodplain/streambank fluxes offers a scalable method for developing spatially explicit models of geomorphic and water quality processes.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.H51D..02N
- Keywords:
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- 1803 Anthropogenic effects;
- HYDROLOGYDE: 1813 Eco-hydrology;
- HYDROLOGYDE: 1871 Surface water quality;
- HYDROLOGYDE: 1879 Watershed;
- HYDROLOGY